/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.coyote.http11.upgrade;

import org.apache.coyote.http11.upgrade.servlet31.ReadListener;
import org.apache.tomcat.util.res.StringManager;

import javax.servlet.ServletInputStream;
import java.io.IOException;

/**
 * Implements the new Servlet 3.1 methods for {@link ServletInputStream}.
 */
public abstract class AbstractServletInputStream extends ServletInputStream {

	protected static final StringManager sm =
			StringManager.getManager(Constants.Package);

	private volatile boolean closeRequired = false;
	// Start in blocking-mode
	private volatile Boolean ready = Boolean.TRUE;
	private volatile ReadListener listener = null;
	private volatile ClassLoader applicationLoader = null;

	/**
	 * New Servlet 3.1 method.
	 */
	public final boolean isFinished() {
		if (listener == null) {
			throw new IllegalStateException(
					sm.getString("upgrade.sis.isFinished.ise"));
		}
		// The only way to finish an HTTP Upgrade connection is to close the
		// socket.
		return false;
	}

	/**
	 * New Servlet 3.1 method.
	 */
	public final boolean isReady() {
		if (listener == null) {
			throw new IllegalStateException(
					sm.getString("upgrade.sis.isReady.ise"));
		}

		// If we already know the current state, return it.
		if (ready != null) {
			return ready.booleanValue();
		}

		try {
			ready = Boolean.valueOf(doIsReady());
		} catch (IOException e) {
			onError(e);
		}
		return ready.booleanValue();
	}

	/**
	 * New Servlet 3.1 method.
	 */
	public final void setReadListener(ReadListener listener) {
		if (listener == null) {
			throw new IllegalArgumentException(
					sm.getString("upgrade.sis.readListener.null"));
		}
		if (this.listener != null) {
			throw new IllegalArgumentException(
					sm.getString("upgrade.sis.readListener.set"));
		}
		this.listener = listener;
		this.applicationLoader = Thread.currentThread().getContextClassLoader();
		// Switching to non-blocking. Don't know if data is available.
		ready = null;
	}

	@Override
	public final int read() throws IOException {
		preReadChecks();

		return readInternal();
	}

	@Override
	public final int readLine(byte[] b, int off, int len) throws IOException {
		preReadChecks();

		if (len <= 0) {
			return 0;
		}
		int count = 0, c;

		while ((c = readInternal()) != -1) {
			b[off++] = (byte) c;
			count++;
			if (c == '\n' || count == len) {
				break;
			}
		}
		return count > 0 ? count : -1;
	}

	@Override
	public final int read(byte[] b, int off, int len) throws IOException {
		preReadChecks();

		try {
			return doRead(listener == null, b, off, len);
		} catch (IOException ioe) {
			closeRequired = true;
			throw ioe;
		}
	}

	@Override
	public void close() throws IOException {
		closeRequired = true;
		doClose();
	}

	private void preReadChecks() {
		if (listener != null && (ready == null || !ready.booleanValue())) {
			throw new IllegalStateException(
					sm.getString("upgrade.sis.read.ise"));
		}
		// No longer know if data is available
		ready = null;
	}

	private int readInternal() throws IOException {
		// Single byte reads for non-blocking need special handling so all
		// single byte reads run through this method.
		byte[] b = new byte[1];
		int result;
		try {
			result = doRead(listener == null, b, 0, 1);
		} catch (IOException ioe) {
			closeRequired = true;
			throw ioe;
		}
		if (result == 0) {
			return -1;
		} else if (result == -1) {
			// Will never happen with a network socket. An IOException will be
			// thrown when the client closes the connection.
			// Echo back the -1 to be safe.
			return -1;
		} else {
			return b[0] & 0xFF;
		}
	}

	protected final void onAllDataRead() throws IOException {
		if (listener == null) {
			return;
		}
		Thread thread = Thread.currentThread();
		ClassLoader originalClassLoader = thread.getContextClassLoader();
		try {
			thread.setContextClassLoader(applicationLoader);
			listener.onAllDataRead();
		} finally {
			thread.setContextClassLoader(originalClassLoader);
		}
	}

	protected final void onDataAvailable() throws IOException {
		if (listener == null) {
			return;
		}
		ready = Boolean.TRUE;
		Thread thread = Thread.currentThread();
		ClassLoader originalClassLoader = thread.getContextClassLoader();
		try {
			thread.setContextClassLoader(applicationLoader);
			listener.onDataAvailable();
		} finally {
			thread.setContextClassLoader(originalClassLoader);
		}
	}

	protected final void onError(Throwable t) {
		if (listener == null) {
			return;
		}
		Thread thread = Thread.currentThread();
		ClassLoader originalClassLoader = thread.getContextClassLoader();
		try {
			thread.setContextClassLoader(applicationLoader);
			listener.onError(t);
		} finally {
			thread.setContextClassLoader(originalClassLoader);
		}
		ready = Boolean.FALSE;
	}

	protected final boolean isCloseRequired() {
		return closeRequired;
	}

	protected abstract boolean doIsReady() throws IOException;

	/**
	 * Abstract method to be overridden by concrete implementations. The base
	 * class will ensure that there are no concurrent calls to this method for
	 * the same socket.
	 */
	protected abstract int doRead(boolean block, byte[] b, int off, int len)
			throws IOException;

	protected abstract void doClose() throws IOException;
}
